Maternal obesity entering pregnancy and excessive gestational weight gain produce substantial morbidity, and both have been rising in prevalence in the past 2 decades. Researchers at the University of Adelaide, Australia, are now funded to begin the largest-by a factor of 10-RCT to limit gestational weight gain among overweight and obese women. The trial will involve state-of-the-art diet and physical activity intervention components to limit weight gain during pregnancy to 0 to 5 kg among a diverse population of 2500 pregnant women. The trial is powered to detect important maternal and infant morbid outcomes based on routinely collected clinical data. Unfortunately, the funding for this trial is not sufficient to collect data on body composition and cardio-metabolic outcomes for mother and child. Yet these biomarker data would be invaluable in elucidating physiologic pathways by which the intervention has its effects, in determining the intervention effect on intermediate maternal outcomes, and perhaps most importantly for the long-term, investigating effects on body composition and cardio-metabolic outcomes among the offspring. The overall goal of this proposal is to assess the effects of an intervention to limit excessive gestational weight gain among overweight and obese pregnant women on markers of adiposity and cardio-metabolic risk in mother, fetus, and newborn. Outcome measures will include Mother: At 28 weeks'gestation, estimated insulin resistance, glucose tolerance, and levels of triglycerides, leptin, adiponectin, and C-reactive protein. Fetus: Change in estimated fetal weight from 18-28 and 28-36 weeks. Newborn: Body fat by air displacement plethysmography and skinfold thicknesses, and cord blood levels of leptin and adiponectin. This proposal reflects a new interdisciplinary collaboration between researchers at Harvard Medical School and the University of Adelaide, with combined expertise in RCTs involving behavior change and in pregnancy, numerous studies of pregnant women and their offspring, and measurement and interpretation of body composition, physiologic, and cardio-metabolic data in mother and child. By obtaining the data from this ancillary study, the trial will be set up not only to provide answers to the proposed aims, but also-with additional funding for follow-up and to take advantage of the stored biosamples-to address numerous questions on long-term health of the mother and the growing child. Limiting excess weight gain during pregnancy among overweight and obese women could help prevent serious health consequences in the mother and child, and a large 4-year randomized controlled trial will begin in mid- 2008 to test this theory. As an ancillary study to the parent trial, the proposed project will add crucial information about the physiology of the mother, the growth of the fetus, and the body composition of the newborn baby. This study will repay its investment many times over by examining how and how well the parent trial works, and by setting up a biological resource that scientists could use to address additional key questions about long-term health of the mothers and children. (End of Abstract)